Batteries have been used for decades to supply power to a variety of different electrical and electro-mechanical devices. Early batteries, referred to as disposable batteries, were simply used until depleted and then discarded and replaced with one or more new batteries. A newer type of battery, referred to as a rechargeable or secondary battery, is capable of being recharged and then reused, therefore offering economic, environmental and ease-of-use benefits compared to a disposable battery.
In a conventional secondary battery, the cap assembly is relatively complex as it is designed to incorporate multiple safety mechanisms. One such safety mechanism is a current interrupt device or CID. The purpose of the CID is to break the electrical connection between the electrode assembly contained within the cell and one of the cell's terminals if the pressure within the cell exceeds a predetermined level. Typically such a state of over pressure is indicative of the cell temperature increasing beyond the intended operating range of the cell, for example due to an extremely high external temperature or due to a failure within the battery or charging system. In addition to disrupting the electrical connection to the electrode assembly, the CID is commonly designed to operate in conjunction with a safety vent integrated within the cap assembly, thereby allowing the built-up gas from the over pressure event to escape the cell.
Another safety mechanism typically incorporated into the cap assembly of a conventional secondary battery is a positive temperature coefficient (PTC) current limiting element. The PTC element is designed such that its resistance becomes very high when the current density exceeds a predetermined level, thereby limiting short circuit current flow.
Although a conventional secondary battery may include multiple safety features, these features are not specifically designed to work in cooperation with whatever housing is eventually used with the battery. Typically such battery housings are designed to accommodate anywhere from a few batteries, e.g., computer battery packs, to hundreds or even thousands of batteries, e.g., hybrid or electric car battery packs. The batteries contained within these housings may be positioned end-to-end, side-by-side, or in some other arrangement. As such, the safety features incorporated into the individual batteries may work as desired or they may have adverse effects on neighboring batteries, for example venting directly into an adjacent battery, thus potentially leading to propagation of the initial battery failure.
Accordingly, what is needed is a battery and a battery pack designed to work together in a cooperative fashion to provide enhanced system performance. The present invention provides such a system.